The invention relates generally to an electronic reprographic printing system, and more particularly concerns a method and apparatus for cleaning the developer units of a color or black and white reprographic printing system and providing for their replenishment with developer.
The marking engine of an electronic reprographic printing system is frequently an electrophotographic printing machine. In an electrophotographic printing machine, a photoconductive member (typically in the form of a belt) is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is thereafter selectively exposed. Exposure of the charged photoconductive member dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoconductive member, the latent image on the photoconductive member is developed by bringing toner into contact therewith. The toner is supplied to the photoconductive member by a developer unit of the magnet roll or brush type. This forms a toner image on the photoconductive member which is subsequently transferred to a copy sheet. The copy sheet is heated to permanently affix the toner image thereto in image configuration.
Multi-color electrophotographic printing is substantially identical to the foregoing process of black and white printing. However, rather than forming a single latent image on the photoconductive surface, successive latent images corresponding to different colors are recorded thereon. Each single color electrostatic latent image is developed with toner of a color complementary thereto and requires its own developer unit. This process is repeated a plurality of cycles for differently colored images and their respective complementarily colored toner. Each single color toner image is transferred to the copy sheet in superimposed registration with the prior toner image. This creates a multi-layered toner image on the copy sheet. Thereafter, the multi-layered toner image is permanently affixed to the copy sheet, creating a color copy.
Regardless of whether color or only monochromatic reproduction is achieved, the developer units employed are often of the magnet roll type, and are described in further detail in U.S. Pat. No. 4,377,334 to Nishikawa, 4,583,112 to Morano et al., and 4,800,411 to Tanaka et al. The contents of each of these three patents is hereby incorporated by reference. Magnet roll developer units use auger or other mixing structure to combine toner with a triboelectrically active carrier to which the toner adheres to produce developer. The developer is enveloped by lines of magnetic force generated by a magnet roll within the developer unit to form a brush-like structure which is swept across the copy material (usually paper). The toner component of the developer is then adhered to the copy; the carrier material is returned to the developer unit for re-use.
After a number of copies, the carrier loses its potency and must be replaced. One way of replacing the carrier involves manually removing the developer unit and relying on gravity and manual mechanical agitation to remove the developer (carrier and commingled toner) from the developer unit. This process is excessively time consuming, even for black and white machines where only one developer unit is present, and can take upwards of 18-20 minutes per developer unit. In a color machine, where four such units are present, the total time required to clean all of the units represents a significant expenditure in machine down-time and labor. There remains a need for a way to clean the developer units with far less down time and greater ease.